CHARACTERIZATION OF THE FRICTION BEHAVIOR OF TABLE TENNIS RUBBERS

Recently, novel polymeric materials (bulk elastomers, elastomer foams, fibers and fiber reinforced composites) were developed and are frequently used for racket sport equipments. These materials reveal highly non-linear, time and temperature dependent mechanical behaviour and the material performance is highly influenced by the environmental conditions (temperature, humidity, pollution). Hence, to support both material development efforts and novel design procedures for high performance racket sport equipments, novel tests methods and procedures to characterize the bulk and surface mechanical behaviour were developed, implemented and applied. The main objective of this paper is the characterization of the surface behaviour of both pimple in and pimple -out table tennis rubbers. Hence, the friction between table tennis ball and rubber surfaces was measured under various sliding motion conditions and the results are described and discussed in the paper. Special emphasis was devoted to the proper definition of the friction and the determination of the main influence parameters on the friction. The rubber friction is widely investigated over a wide range of test conditions and is described and the results discussed in many scientific papers. The main driving force of these investigations was the characterization of tire rubber friction/traction under dry and especially wet conditions. The friction force for rubber is a sum of the contribution of two essentially different physical processes; the adhesion between rubber and solid counterpart and the deformation of the elastomers which is described as the hysteretic deformation of the rubber F-r = F-adh + F-hyst Where F-r is the friction force, F-adh the adhesion force component and F-hyst is the hysteretic deformation force component. While the hysteretic component can be derived from the dynamic mechanical test performed and described in the previous paper, the determination of the adhesion component remains a challenging task. To gain more insight into the complex surface behaviour of rubbers friction tests were performed using a universal microtribometer (UMT, CETR, Campbell, CA, USA). The table tennis ball was glued into a fixture and this was positioned in the upper moving part of the UMT. The test specimen was the rest of the cut table tennis rubber sponge and was glued to a steel plate fixed in the lower stationary drive of the UMT. The table tennis ball was first pressed with a controlled normal force (F-z) into the rubber surface and subsequently a linear sliding motion with controlled rate was applied. The normal force was varied as 1, 2, 5 and 10 N and the sliding rate was 0.1 and 1 mm/s in the experiments. Both the normal (F-z) and the friction force (F-x) was continuously measured and recorded during the test. The coefficient of friction (COF) was then calculated in the test software. The results of these investigations are described and discussed as: center dot Influence of the normal load and sliding rate on the friction behaviour of table tennis rubbers, center dot Effect of the surface cleanness on the friction behaviour, center dot Recognition of the modification of the surface by additional treatment and center dot Comparison of the friction characteristic of various commercial table tennis rubber sponges.